Many geological, biological, man-made and other solid materials are heterogeneous composite structures formed from interrelated, but microscopically and chemically discrete entities, such as particles or cells. If an analysis of the chemical or physical properties of this type of composite sample is desired, the analysis method and device must address these various microscopic entities. The primary objectives of an analysis of the properties of these composite samples are to: 1) locate and identify the physical structure of each type of particle within one sample; 2) identify the chemical or other properties of that particle type; 3) identify the physical relationships among the various particle types within the sample; and 4) be capable of analyzing a wide variety of particle types. The analyzer device should also be light weight, rugged in construction, low in cost, and easy to operate. The process using the analyzer should also be capable of several active analyzing and storage modes. These include: an on-line analysis mode, an off-line analysis mode, a temporary rest mode, and a long term storage mode. A minimum of effort to convert from one mode to another is also desirable.
Most of the current analyzers may accomplish some of these objectives well, but other objectives are accomplished poorly or not at all. A common analysis technique involves splitting the sample. A small sample portion is prepared for optical analysis (microscopic examination), while a second portion is prepared for a separate bulk chemical analysis, for example bulk analysis by pyrolysis. This two step process, however tends to be slow, complex, and unreliable. In addition, the bulk analysis step obscures the chemical properties of each particle as well as the relationships among the particles which comprise the composite sample, i.e., a sample composed of diverse particles. The bulk chemical analysis yields information from all particles producing significant pyrolyzates within the sample. It may not be possible to reconstruct the contribution(s) of each type of particle from the mixed particle pyrolyzate information generated by this bulk analysis approach.
The bulk analysis process step typically requires crushing, placing the crushed sample in an enclosed container, heating the crushed sample to elevated temperatures which generates a pyrolyzate fluid, and transporting the fluid to a chemical "bulk analysis" device. The enclosed container and heating device may also be part of the "bulk analysis" device. The chemical "bulk analysis" device may be a gas-liquid chromatograph, or a mass spectrometer or a nuclear resonance spectrometer. An example of devices used for this pyrolysis analysis method, without any means for optical viewing, can be found in U.S. Pat. No. 4,408,125.
This "bulk" method generates measurable quantities of pyrolyzates from groups of microscopic particles within a composite sample which individually could not generate sufficient pyrolyzates for chemical analysis. The bulk pyrolysis process can also be applied to large individual or groups of similar particles separated from the composite sample. However, physical or chemical separation of microscopic particles prior to pyrolysis is difficult, e.g., density gradient centrifugation. Furthermore, separation can alter the chemical and physical properties of the microscopic particles and destroy the relationships among these particles.
As an alternative to ordinary heating (pyrolysis or thermal extraction) sources, a laser beam can be used as a source of thermal energy or heating. This is illustrated in U.S. Pat. Nos. 4,025,790 and 4,672,169. The processes described in these patents are for gases, not particles. The laser selectively excites (i.e., the laser beam's infrared energy is absorbed by) certain gaseous compounds in a mixed sample within an enclosed chamber. Laser beam heating has several advantages. It allows for directing heat into a specific zone and rapidly heating (i.e., more quickly heating than conventional sources of heat) the specific gaseous compounds of interest.
The separate microscopic and thermal extraction or pyrolysis bulk analysis approach requires sample transport between the microscopic examination and the heating/pyrolyzate analyzer devices. The multi-step approach also tends to limit the speed and use of devices in this sequential step type of analysis. One can also never be sure that the spit sample portions are identical for composite samples. Reconstruction of each type of pyrolyzate producing particle present in the composite sample from the bulk information produced, even if possible, can also be unreliable.
An integrated optical and pyrolysis approach is also known. One integrated approach modifies a laser heating pyrolysis system by adding a microscope. The sample is placed in a pyrolysis chamber which includes a window for microscopic examination and laser beam transmission. In addition, other equipment may be required to allow optical focusing, illumination, and sample viewing placement, removal, and manipulation.
The optical modifications to the basic pyrolysis chamber design compromise the performance of both the optical and pyrolysis analysis systems. For example, the combined device must: 1) accommodate the transmission of the narrow laser beam and the microscope's broader light beam or field of view; 2) allow for the proper sample focusing of the laser beam and optical microscope systems; 3) allow sufficient space between the sample and the window to avoid window clouding and overheating from contact with the hot pyrolyzates, but be close enough to avoid changing the focal lengths of each system; and 4) provide a chamber large enough to include the added components but not so large as to dilute or ineffectually collect the small quantities of pyrolyzates which may be produced. In addition, the multiplicity of elements required to accomplish both analyses tends to get in the way of each other in the confined space of a pyrolysis chamber. This further limits operational use, reliability and flexibility. These problems also tend to limit the combined analysis device to specific sample sizes and particle types.
A second method, which is the inverse of this first integrated approach (modifying a pyrolysis system), converts an optical system (microscope). The optical system is modified to include a colinear heating laser beam and an open sided chamber. The open side of the chamber is placed on a conventional glass slide on the microscope stage. The remainder of the system includes a chamber window, a supply of a purge gas, and a collection tube. This second or inverse integrated approach is illustrated in U.S. Pat. No. 3,941,567. However, this inverse approach also requires design compromises similar to the first integrated approach.
A specific sample of the integrated approach design comprises and problems occurs if analysis of a single type of particle within a composite sample is desired. Focusing of the pyrolyzing laser beam requires a narrow beam, smaller than the representative dimension of the particle. The laser beam or particle location must also be adjustable, so that the beam may be pointed or aimed at the spot on the particle of interest. The adjustment may also require refocusing of both the microscope and laser systems. Very small individual particles may not be capable of generating sufficient pyrolyzate upon laser beam heating to be detected by an analyzer, even if the beam is narrow and properly focused. These problems may limit the application of this combined laser and microscope system to only larger particles within the composite sample.
The collection of the hot gaseous pyrolyzate fluids also presents problems. Hot pyrolyzate gases tend to condense on any cooler (i.e., ambient) temperature surfaces of the chamber. Heating the chamber may prevent condensation, but can lead to optical distortions, thermal expansion, seal failures, and outgassing of chamber materials, and pyrolysis of other particles (causing bulk release and contamination of the analysis).